1. Field of the Invention
The present invention relates to the structure of a jig for supporting wafers and, more particularly, to the structure which can relieve a decline in precision of wafer processing.
2. Description of the Prior Art
In manufacturing process of integrated circuits, impurities such as ions are doped to the surface of a silicon wafer or the like, and then made to diffuse therein. A diffusion layer thus formed is used for forming circuit elements of the integrated circuit. When performing above diffusion, wafers are first set into a heating furnace with impurities doped thereon. Then the furnace is filled with gas or the like, and heating is carried out under high temperature.
The heating furnace contains a large number of wafers so as to allow simultaneous heat-treatment. Wafers at this step are supported by the jig and set into the heating furnace. A conventional wafer jig is shown in a general perspective view in FIG. 1A. This wafer jig 40 is for a vertical heating furnace, made up of a roof plate 41, a bottom plate 42, and four pillars 43 for fixing the roof plate 41 and the bottom plate 42. Wafers 30 are put in at regular intervals between the roof plate 41 and the bottom plate 42.
Support of wafers 30 is conducted as follows. Each pillar 43 is provided with a plurality of recessed parts 49, as shown in FIG. 1B. This structure allows each wafer 30 to be inserted in each recessed part 49 and supported there. FIG. 1C shows in a plane view the state in which the wafer is supported by four pillars 43.
However, the conventional wafer jig has the following problems. First, although using a wafer of large size is effective for efficient manufacture of integrated circuits, such a large-sized wafer 30 is liable to curve or warp due to its own weight when supported by four pillars 43.
Second, integrated circuits should be processed with strict precision. Particles (dust) or the like are possible contaminant against the processing surface, making final products less reliable. The conventional wafer jig 40 of FIG. 1 allows wafers 30 to be placed at close intervals from each other. As a result, if particles contaminate one wafer 30 at the back thereof, they may fall onto the processing surface of another wafer 30 thereunder. Particles thus added on the processing surface are responsible for a decline in precision of wafer processing, allowing final products to be less reliable, as described above.
Moreover, gas flow is made to disturb near each pillar 43, because wafers 30 are directly supported by pillars 43. In other words, gas is not uniformly supplied in the vicinity 48 of recessed parts 49 where wafers 30 are inserted thereto and make contact with pillars 43. Consequently, wafer processing is not conducted as desired, leading to the problem of a decline in precision of wafer processing.